This project entails the development and application of methods for analyzing the genetic basis for specificity of transplantation and other T cell reactions in the rat. Specifically reactive T cells are prepared by repeated stimulation of lymphocytes with major transplantation antigens. The cross reactivity of these cells on other histocompatibility antigens and conventional antigens is then measured. Furthermore these specifically selected cells will then be used as antigen in the anticipation of raising antibodies against their specific receptors for antigen. The genetic basis for receptor specificity will be analyzed. Anti-idiotypic antisera will be raised using homogeneous alloantibodies prepared by hybrid cell fusion. The target for such anti-idiotypes will be sought on T and B cells, and the genetic basis of their expression analyzed.